Block downstream policy
The Block downstream policy prevents updates from downstream registries (i.e. disallows push/publish to a registry with this policy enabled). The policy also prevents manual uploads of packages.
A registry with the policy enabled can still pull new package versions upstreams.
Cache / firewall registries
Registries that (only) manage incoming packages where users want to block packages from downstream registries. Preventing accidental publish of internal packages to such registries.